Polymethylpolysiloxane thickened phenylmethyl silicone oil



United States Patent POLYMETHYLPOLYSILOXANE THICKENED PHENYLMETHYLSILICONE OIL George V. Browning, Schenectady, N. Y., and Cecil Brannen,Munster, Ind., assignors to Standard Oil Company, Chicago, Ill., acorporation of Indiana No Drawing. Application April29, 1952, Serial No.285,080

8 Claims. (Cl. 252-49.6)

The present invention relates to novel lubricant greases and to themethod of preparing same. More particularly it relates to novel greaseswherein both the lubricant-vehicle and the thickening agent compriseorganosilicon compounds.

Very high temperatures resulting from high speed operation of machines,engines, etc. have resulted in a great need for lubricant greases whichare stable at such temperatures, and the requirements of lubricants ofthis type are more and more difficult to fulfill as the temperaturesencountered become progressively higher. The art has progressed from theuse of petroleum lubricant vehicles in such greases to silicone polymeroils which are capable of withstanding much higher temperatures andsince the thickening agents heretofore employed, e. g. lithium soaps ofhigh molecular weight carboxylic acids and the like cannot withstandsuch temperatures, more stable thickeners are likewise required.Lubricant greases have been produced recently by milling a thickener gelprepared from dimethyldichlorosilane and methyltrichlorosilane withdimethyl silicone liquids having lubricating properties, but certainproblemshave been encountered therewith, viz., a difiiculty in obtaininga smooth homogeneous product and relative stability at hightemperatures. Thus, despite the chemical similarity of the gel and thesilicone polymer vehicle, such materials cannot be combined readily toproduce a smooth homogeneous product by usual milling operations and itappears that unreacted--OH groups in such a gel and the consequentresidual functionality resulting therefrom are responsible for theinstability thereof at elevated temperatures, e. g. 200 F. and above.

It is a primary object of the present inventionto provide an improvedmethod of preparing lubricant greases wherein both the thickening agentand the lubricant vehicle are organo-silicon compounds. A further objectis to provide a method of preparing an organo-silicon thickening agent,for use in grease manufacture, which can readily be milled with organosilicon lubricant vehicles to yield smooth greases having excellent hightemperature stability. A still further object is to provide novelorgano-silico-n greases which are stable and retain effectivelubricating properties at elevated temperatures. Additional objects willbe apparent from the ensuing description of the present invention.

Greases of the present invention are prepared by thickening liquidorgano-silicon polymers having lubricating properties to greaseconsistency by means of novel organo-silicon thickening agents. Suchthickening agents or gels, as they may be referred to alternatively, areprepared by heating polymethylpolysiloxanes having substantially noresidual functionality to a temperature in the range of from about 400F. to about 550 F. in the presence of a stable liquid organo-siliconpolymer, e. g. phenylmethylsilicone oil, for a period of time which isdependerit upon temperature and other factors which will hereinafter bemore fully described. A polysiloxane has nolresidual functionality, forpurposes of the present.

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invention, when it has substantially no tendency to react further withitself or other siloxa-nes because of the presence of unreacted -OHgroups in the polymer. The polymethylpolysiloxanes, which may be heatedto form thickener gels suitable for use in accordance herewith, may beeither linear or branched, i. e. they may comprise essentially straightchain polymers derived principally from dimethyldichlorosilane ordimethyldiethoxysilane, or they may be cross-linked polymers resultingfrom the cohydrolysis of two or more methylchloroormethylethoxysilan-es. Such chains are freed from residual functionalityby cohydrolyzing therewith a relatively small amount of amono-functional silane, viz. trimethylchlorosilane ortrimethylethoxysilane.

When polymethylpolysiloxanes are heated to a temperature in the aboveindicated range it appears to result in their oxidation and thermalrearrangement, with gels prepared from either linear or branched chainpolysiloxanes being substantially cross-linked. Such cross-linking ispotentially desirable inasmuch as the lattice thus formed should serveas an excellent framework into which the lubricant vehicle may beimbibed, but it has been found, surprisingly enough, that unless the gelis prepared in the presence of a stable silicone liquid such asphenylmethyl silicone polymer the manufacture of smooth greases isditficult if not impossible. A silicone lubricant vehicle and athickener gel prepared in the absence of a stable silicone liquid cannotbe milled together satisfactorily, apparently because the lubricantvehicle is not readily imbibed into the gel. When, however, a stableliquid polymer is uniformly distributed throughout the lattice structureduring formation thereof, imbibition of the lubricant vehicle into thegel is effectively promoted during the milling operation. A liquidpolymer must be employed for this purpose which is not oxidized orthermally rearranged to any substantial extent under the conditionsencountered and which will serve to promote the rapid and smoothadmixture of gel and lubricant vehicle by uniformly blending with suchlubricant vehicle and promoting its inhibition. For this purpose, aphenylmethylsilicone liquid in the lubricant viscosity range ispreferred, although other organo-silicon liquids which are stable at theelevated temperatures may likewise be employed. The liquidorgano-silicon polymer may be mixed with the polysiloxane to be gelledjust prior to heating same or it may be combined in the initialhydrolysis of the various silanes.

An amount from about 2% to about 60% and preferably from about 10% toabout 30% by weight of the mixture subjected to heating should comprisestable silicone, e. g. phenylmethylsilicone. l-f phenylmethylsiliconeliquid or other suitable stable silicone liquid is to be employed as thetotal lubricant vehicle, it may be present in its entirety during theheating step, but it is preferred from the standpoint of economy, bothof time and energy, to prepare the gel with a lesser quantity and thento mill same with the remaining portion of the vehicle. The insulatingefiect of a large quantity of thermally stable liquid, such asphenylmethylsilicone, greatly retards the formation of the gel andconsequently requires longer heating times.

Although the present invention does not reside in either th method ofpreparation of the polysiloxanes from which our thickener gels areprepared or the composition of such polymers, it is preferred to employan aqueous-ether medium for carrying out the hydrolysis of the silanesbecause of proven excellent results obtainable therewith. Furthermore,it is essential that minimum quantities of certain silanes be presentduring hydrolysis in order to obtain sufficient chain formation; thus,it is necessary, in accordance herewith, to employ at least a minimumamount of dimethyldichlorosilane or dimethyldiethoxysilane as theprimary chain former along with a minimum quantity oftrimethylchlorosilane or trimethylethoxysilane to inhibit chainformation and assure substantial elimination of residual functionality.Varying amounts of methyltrichloroor methyltriethoxysilane may or maynot be present as well. Rochows Chemistry of the Silicones (Wileyl95l),which goes into considerable detail with respect to preparativetechniques, coupled with the illustrative examples hereinafter set fortheliminates the necessity for further detailed discussion thereof.

In accordance with the present invention, therefore, the thickener gelis prepared by heating in the presence of a stable liquid organo-siliconpolymer, polysiloxanes resulting from the hydrolysis of a mixturecomprising about 30% to about 90% and preferably from about 45 to about70%, of dimethyldichlorosilane or dimethyldiethoxysilane, from to about70% and preferably from about 25% to about 50% of methyltrichlorosilaneor methyltriethoxysilane, and from about to about 70% and preferablyfrom about to about 30% of trimethylchlorosilane ortn'methylethoxysilane. Such polysiloxanes should be heated to atemperature in the range of from about 400 F. to about 550 F. for aperiod of from about 2 hours to about 72 hours depending upon thetemperature employed and preferably for a period of from about hours toabout 40 hours at temperatures in the range of from about 450 F. toabout 500 F. in order to produce a suitable gel for use in accordanceherewith. It should be understood that longer time is required at lowertemperatures and that at the higher temperatures the gels are formedmore quickly. Furthermore, the larger th percentage of stable siliconepresent, the longer the time required at any given temperature.

The amount of gel, prepared in accordance herewith, which is required tothicken a silicone lubricating viscosity range oil to grease consistencyvaries over a relatively wide range depending upon the consistency ofthe grease desired and the composition of the particular gel. If, forexample, the gel is prepared from a mixture comprising a relativelylarge amount of stable phenylmethylsilicone liquid, a greater percentageof that gel is required to produce a grease in admixtures with asilicone oil inasmuch as such a gel already embodies a rather large partof the lubricant vehicle in its lattice. In accordance herewith,therefore, greases of the present invention may be prepared by millingan amount of from about 10% to about 80% and preferably from about 20%to about 60% of a gel prepared in accordance with the present inventionwith a silicone liquid in the lubricating viscosity range of the typehereinafter more fully defined.

The silicone polymer oils useful as th lubricant vehicles in accordancewith the present invention, as distinguished from the thermally stablephenylmethyl silicone or the like, which must be heated with the gel,have the following unit structure:

B one] it wherein R and R represent alkyl, aryl, alkylaryl, aryalkyl andcycloalkyl groups. Such compounds may be produced by well-known methods,e. g. the hydrolysis of dialkyldichlorosilanes ordialkyldiethoxysilanes. For purposes of the present invention, onlythose polymers which are high boiling liquids within th lubricating oilviscosity range are suitable, these generally possessing a viscosity at100-F. which is within the range of from about 10 to about 600centistokes. Such products are generally colorless and inert, have verylow volatility and undergo relatively slight change in viscosity for agiven change in temperature. Relatively common oils of this type aredimethylsilicone polymer, phenylmethylsilicone polymer,chlorophenylmethylsiliconepolymer, etc., it being preferred to employthe phenylmethylsilicone polymer in accordance herewith. Methods ofpreparing such compounds are taught in numerous patents, e. g. U. S.2,410,346, U. S. 2,456,496, and in the literature such as Chemistry ofthe Silicones by Rochow, page 61, et seq. A particularly desirablephenylmethylsilicone polymer for use in accordance with the presentinvention is Dow-Corning 550 silicon fluid, a product of Dow- Corning,Inc., which has a viscosity at 77 F. of about 100 to 150 centistokes. Asindicated above, it is preferred that the organo-silicon polymer oilemployed as promoter and which is incorporated with the polysiloxanesduring the heating step be the same as that with which the resulting gelis milled to produce a grease, but this is not necessary and differentpolymers may be employed. Thus, for example, phenylmethylsilicone oilmay be employed as the promoter liquid and after formation of the gel,under conditions hereinabove set forth, the gel may be milled with amethylsilicone oil to produce a grease.

As indicated in the Chemistry of the Silicones by Rochow (1951), page 78et seq., various theoretical and practical possibilities exist for thpreparation of crosslinked polysiloxanes of the type herein describedand whereas the initial reactants are preferably themethylchlorosilanes, the methylethoxysilanes may likewise be used toproduce the desired gel.

In order that those skilled in the art may better understand how thpresent invention may be carried into efiect, the following illustrativeexamples are given. In the following examples the temperatures given arethose determined by means of a thermocouple attached to the electricalheating mantles employed and are known to be substantially higher thanthe temperature of the material being heated, particularly in thosecases where a short period of time was employed and opportunity forequilibrium is not available.

Example 1 A mixture of 100 g. of methyltrichlorosilane, 100 g. ofdimethylchlorosilane, 20 g. of trimethylchlorosilane, 80 g. ofDow-Corning 550 silicone fluid, and 500 ml. of ethyl ether was pouredonto about 500 g. of ice and the layers were separated. The volatilematerial was distilled olf and the residue baked at a thermocouplereading of 600 F. for two hours to give a white gel. Previous experiencewith the heating mantle would indicate that a pot temperature of about550 existed. This gel and 50 additional grams of Dow-Corning 550silicone fluid were mixed and passed through a colloid mill to give asmooth white grease. When passed through a mesh screen in a Hainmicroworker, the following micropenetrations were measured:

Worker strokes: Penetration 0 254 Example 2 Example 3 g. ofdimethyldichlorosilane, 100 g. of methyltrichlorosilane, 50 g. oftrimethylchlorosilane and 12.5 g. of Dow-Corning 550 oil were hydrolyzedin a manner similar to that set forth in Example 1 and after removingthe ether the resulting hydrolysis product was heated to 400 F. for aperiod .of about 70 hours to produce a white gel. This gel was thenmilled with 30 g. of DC 550 oil and milled in a roller mill to produce asmooth homogeneous grease.

Example 4 In comparison to the grease of Example 2, 100 g. ofDow-Corning 200 were heated to a temperature of 500 F. for a period of30 hours during which time air was continuously bubbled therethrough.The white gel which resulted had essentially the same appearance as thatof Example 2 but could not be readily milled With 50 g. of Dow-Corning550 oil and the product resulting therefrom a grainy, lackedhomogeneity, and was extremely lumpy.

It should be understood, with respect to the temperature range in whichthe gels of the present invention may be prepared, that below about 400F. any gelation which might occur would take too long to be practicaland that above about 550 F. the possibility of incipient decompositionof the organo-silicon constituents exists, particularly the thickenedpolymethylpolysiloxane.

The percentages recited in the above description and appended claims areby weight unless otherwise indicated.

Having thus described the present invention, what we claim as new anddesire to secure as Letters Patent of the United States is:

l. The method of preparing a homogeneous thermally stableorgano-silicone polymer grease consisting essentially of a thermallystable organo-silicone polymer having a viscosity in the lubricating oilrange of from about to about 600 centistokes at 100 F. thickened togrease consistency with a gelled polymethylpolysiloxane, comprisingmixing from about 40% to 98% of a liquid polymethylpolysiloxanesubstantially free of unreacted OH groups with from about 2% to about60% of a liquid organo-silicone polymer, other than saidpolymethylpolysiloxane, thermally stable at temperatures up to about 550F. and having a viscosity in the lubricating oil range of from about 10to about 600 centistokes at 100 F., heating said mixture to atemperature in the range of from about 400 F. to about 550 F. for aperiod of from about 1 hour to about 72 hours to form a gelled mixture,and milling the resultant gelled mixture with a sufiicient amount of athermally stable organo-silicone polymer having a viscosity in thelubricating oil viscosity range of from about 10 to about 600centistokes at 100 F. to form a homogeneous grease containing from about10% to about 80% of said gelled mixture. I

2. A homogeneous thermally stable grease prepared by the method of claim1.

3. The method of preparing a homogeneous thermally stableorgano-silicone polymer grease consisting essentially of a phenylmethylsilicone polymer having a viscosity in the lubricating oil viscosityrange of from about 10 to about 600 centistokes at 100 F. and apolymethylpolysiloxane, comprising mixing from about 40% to about 98% ofaliquid polymethylpolysiloxane substantially free of unreacted OH groupswith from about 2% to about 60% of a phenylmethyl silicone liquid stableat a temperature of about 550 F. and having a viscosity in thelubricating oil range of from about 10 to about 600 centistokes at 100F., heating said mixture to a temperature in the range of from about 400F. to about 550 F. for a time sutficient to form a gelled mixture, andmilling the resultant gelled mixture with a suflicient amount of athermally stable organo-silicone polymer having a viscosity in thelubricating oil viscosity range of from about 10 to about 600centistokes at 100 F. to form a homogeneous grease compositioncontaining from about 10% to 80% of said gelled mixture.

4. A homogeneous thermally stable grease prepared by the method of claim3.

5. The method of preparing a homogeneous thermally stableorgano-silicone polymer grease, consisting essentially of a thermallystable organo-silicone polymer, havinga viscosity in the lubricating oilrange of from about 10 to about 600 centistokes at 100 F., thickened togrease consistency with a gelled liquid polymethyl-polysiloxane,comprising mixing from about 2% to about 60% of a liquidor'gano-silicone polymer, thermally stable at a temperature up to about550 F. and having a viscosity in the lubricating oil range of from about10 to about 600 centistokes at 100 F., with from about 40% to 98% of amixture comprising, from about 30% to about 90% of a silane selectedfrom the group consisting of dimethyldichlorosilane anddimethyldiethoxysilane, from 0% to about 70% of a silane selected fromthe class consisting of methyl trichlorosilane and methyltriethoxysilane, and from about 10% to about 70% of a silane selectedfrom the group consisting of trimethyl chlorosilane andtrimethylethoxysilane, cohydrolyzing said mixture in an aqueous-ethermedium to obtain a resultant mixture of a polymethylpolysiloxanesubstantially free of unreacted --OH groups, and said organosiliconepolymer, heating said resultant mixture to a temperature in the range offrom about 400 F. to about 550 F. for a time suflicient to form a gelledmixture, and milling said gelled mixture with a sufiicient amount of aliquid organo-silicone polymer, having a viscosity in the lubricatingoil viscosity range of from about 10 to about 600 centistokes at 100 F.and thermally stable at a temperature up to about 550 F., to formahomogeneous grease composition containing from about 10% to of saidgelled mixture.

6. The method of claim 5 in which the organo-silicone polymer is aphenylmethyl silicone.

7. The method of preparing a homogeneous thermally stableorgano-silicone polymer grease, consisting essentially of a thermallystable organo-silicone polymer, having a viscosity in the lubricatingoil range of from about 10 to about 600 centistokes at 100 F., thickenedto grease consistency with a gelled liquid polymethyl-polysiloxane,comprising mixing from about 2% to about 60% of a liquid organo-siliconepolymer, thermally stable at a temperature up to about 550 F. and havinga viscosity in the lubricating oil range of from about 10 to about 600centistokes at 100 F., with from about 40% to 98% of a mixturecomprising from about 30% to about of dimethyldichlorosilane, from 0% toabout 70% of methyltrichlorosilane, and from about 10% to about 70% oftrimethylchlorosilane, cohydrolyzing said mixture in an aqueous-ethermedium to obtain a resultant mixture of a polymethyl polysiloxanesubstantially free of unreacted OH groups, and said organo-siliconepolymer, heating said resultant mixture to a temperature in the range offrom about 400 F. to about 550 F. for a time sufiicient to form a gelledmixture, and milling said gelled mixture with a sufficieut amount of aliquid organosi-licone polymer having a viscosity in the lubricating oilviscosity range of from about 10 to about 600 centistokes at 100 F. andthermally stable at a temperature up to about 550 F., to form ahomogeneous grease composition containing from about 10% to 80% of saidgelled mixture.

8. A homogeneous thermally stable grease prepared by the method of claim7.

References Cited in the file of this patent UNITED STATES PATENTS2,258,218 Rochow Oct. 7, 1941 2,397,727 Daudt Apr. 2, 1946 2,407,181Scott Sept. 3, 1946 2,443,353 Hyde et al. June 15, 1948 2,460,457 HydeFeb. 1, 1949 2,460,795 Warrick Feb. 1, 1949 (Other references onfollowing page) UNITED STATES PATENTS I 2,561,178

Daudt May 3, 1949 2, 45,5 3 Hyde Oct. 25, 1949 Pederson Nov. 1, 1949Daudt Apr. 24, 1951 365,3

, Burkhard July 17, 1951 Hunter et a1 Oct. 21, 1952 Barry' July 14, 1953FOREIGN PATENTS Germany Feb. 2, 1953

1. THE METHOD OF PREPARING A HOMOGENEOUS THERMALLY STABLEORGANO-SILICONE POLYMER GREASE CONSISTING ESSENTIALLY OF A THERMALLYSTABLE ORGANO-SILICONE POLYMER HAVING A VISCOSITY IN THE LUBRICATING OILRANGE OF FROM ABOUT 10 TO 600 CENTISTOKES AT 100* F. THICKENED TO GREASECONSISTENCY WITH A GELLED POLYMETHYLPOLYSILOXANE, COMPRISING MIXING FROMABOUT 40% TO 98% OF A LIQUID POLYMETHYLPOLYSILOXANE SUBSTANTIALLY FREEOF UNREACTED -OH GROUPS WITH FROM ABOUT 2% TO ABOUT 60% OF A LIQUIDORGANO-SILICONE POLYMER, OTHER THAN SAID POLYMETHYLPOLYSILOXANE,THERMALLY STABLE AT TEMPERATURES UP TO ABOUT 550* F. AND HAVING AVISCOSITY IN THE LUBRICATING OIL RANGE OF FROM ABOUT 10 TO ABOUT 600CENTISTOKES AT 100* F., HEATING SAID MIXTURE TO A TEMPERATURE IN THERANGE OF FROM ABOUT 400* F. TO ABOUT 550* F. FOR A PERIOD OF FROM ABOUT1 HOUR TO ABOUT 72 HOURS TO FORM A GELLED MIXTURE, AND MILLING THERESULTANT GELLED MIXTURE WITH A SUFFICIENT AND MILLING THE RESULTANTGELLED MIXTURE WITH A POLYMER HAVING A VISCOSTIY IN THE LUBRICATING OILVISCOSITY RANGE OF FROM ABOUT 10 TO ABOUT 600 CENTISTOKES AT 100* F. TOFORM A HOMOGENEOUS GREASE CONTAINING FROM ABOUT 10% TO ABOUT 80% OF SAIDGELLED MIXTURE.